The platinum 5 min in TCCC: Analysis of junctional and extremity hemorrhage scenarios with a mathematical model

Abstract

Introduction To achieve the aim of zero preventable deaths on the battlefield a deeper understanding of uncontrolled hemorrhage from junctional or proximal extremity sources is mandatory. While tourniquet application to the extremities has drastically reduced morbidity and mortality, there is still room for improvement regarding the timing of tourniquet placement as the available evidence clearly points out a tight correlation between timing of tourniquet application and outcome. To save as many lives as possible the "point of no return" regarding the circulatory breakdown due to hemorrhage, colloquially addressed as platinum 5 min, needs to be determined. As clinical analysis or controlled studies are difficult, if not impossible, and animal experiments cannot be translated to bleeding in humans, we present a mathematical modeling approach. The key assumption of the model is that hemodynamics in the early phase of massive hemorrhage are determined by the cardiac function, the passive physical properties of the vascular system, that is, compliances etc., as humoral compensatory mechanisms kick in at a later point in time, and the baroceptor reflex, which constitutes the immediate response to volume loss. Materials and Methods A lumped mathematical model based on differential equations describing three distinct arterial and two venous compartments, the heart and the baroceptor mechanism is developed. With this model, different patterns of blood loss (%) and duration of bleeding (s) are simulated: 10%/30 and 60 s, 20%/30 and 60 s, 30%/30, 60 and 120 s, and 35%/30, 120 and 180 s. These bleeding patterns are chosen such that they resemble clinically scenarios following junctional and proximal extremity injuries. Results Three hemodynamic patterns can be distinguished. The system stabilizes on a lower blood pressure level (10%/30 and 60 s, 20%/30 and 60 s), the system formally stabilizes on a very low level, which is physiologically not reasonable (30%/30, 60 and 120 s), the system irreversibly breaks down with no signs of restabilization (35%/30, 120 and 180 s). Conclusion Thus the immediacy of intervention in terms of application of a tourniquet is clearly emphasized by the simulation, that is, the window of opportunity for a life-saving intervention, especially in a combat setting, is significantly smaller than the symbolic "platinum five minutes" might suggest. With respect to the 3-min window of opportunity identified in the simulations the effective application of these devices in a TCCC setting appears questionable. Given these observations, further research and development into solutions that allow the timely identification of a junctional bleeding problem and application of compression is necessary.